This invention relates to a vehicle brake hydraulic pressure generator in which the hydraulic pressure supplied from a hydraulic pressure source including a power-driven pump is adjusted by a pressure adjusting valve to a value corresponding to the brake operating force and outputted to a first hydraulic line, the output hydraulic pressure is used to activate a master cylinder, and the hydraulic pressure generated by the master cylinder is given to a second hydraulic line that is independent of the first hydraulic line, and if the first hydraulic line fails, the brake operating force is directly transmitted to the master cylinder to activate it.
As a brake hydraulic pressure generator of this type, there are ones disclosed in JP patent publication 61-37140 and European patent EP1078833A2.
The device of the former publication applies brake operating force from a brake pedal to an operating rod inserted in a booster piston and transmits the brake operating force to an input rod in the booster piston through a stroke-limiting spring. The input rod closes an outlet valve and opens an inlet valve to adjust the hydraulic pressure fed by a pump into a pressure accumulating chamber in front of the booster piston and the hydraulic pressure is outputted to a first hydraulic line. The output hydraulic pressure after adjusted is also used as pressure for activating the master cylinder to output the hydraulic pressure generated in the master cylinder to a second hydraulic line. In this device, if the hydraulic pressure source having a power-driven pump fails, the brake operating force applied to the operating rod is directly transmitted to a piston of the master cylinder through the stroke limiting spring, input rod, booster piston and a tappet rod mounted on the booster piston, so that hydraulic pressure corresponding to the brake operating force is generated in the master cylinder.
The device of the latter publication includes an auxiliary piston and a simulator piston corresponding to the operating rod of the first-mentioned device. The brake operating force applied to the simulator piston is transmitted to the auxiliary piston through a stroke-imparting elastic member (spring and rubber). The hydraulic pressure supplied from a hydraulic pressure source having a pump is adjusted by means of a pressure adjusting valve of which the operating condition changes with displacement of the auxiliary piston, to a value corresponding to the brake operating force, and the master cylinder is activated by the hydraulic pressure after adjusted. In this device, too, if the hydraulic pressure source fails, the brake operating force is directly transmitted to the master cylinder.
In the brake hydraulic pressure generator of JP patent publication 61-37140, which uses a brake booster, a stroke corresponding to the brake operating force is imparted to the operating rod by the stroke-limiting spring even during failure of the hydraulic pressure source. Since it becomes an unavailable stroke, during failure of the hydraulic pressure source, in order to obtain a sufficient braking force, a long operating stroke to which is added the unavailable stroke is needed.
On the other hand, in the device of EP1078833A2 publication, when the auxiliary piston moves by more than a predetermined stroke relative to the casing, a communicating passage between the simulator chamber formed in front of the simulator piston and the atmospheric reservoir is shut off. During failure of the hydraulic pressure source, hydraulic pressure that balances with the brake operating force is not applied to the auxiliary piston, so that shutoff of the communicating passage occurs earlier and brake fluid is sealed in the simulator chamber. This restricts the stroke of the simulator piston, so that it is possible to produce a sufficient braking force with a short operating stroke.
But if the hydraulic pressure source fails during brake operation, the communicating passage is shut off in a situation where the simulator piston is ordinarily making a stroke, so that even if quick return of the brakes is carried out thereafter, return of the auxiliary piston, which is dependent upon the master cylinder, is delayed. Thus, the communicating passage is kept shut, so that the simulator piston will not return to the original position. Thus, if quick operation of the brake is carried out followed by quick return, the non-returned amount of the simulator piston will become an unavailable stroke, so that the operating stroke for ensuring a sufficient braking force becomes long.
An object of the invention is to ensure a sufficient braking force with a short operating stroke even if the hydraulic pressure source or a hydraulic line connecting thereto should fail.
This invention proposes to improve a vehicle brake hydraulic pressure generating device comprising a hydraulic pressure source for generating a predetermined hydraulic pressure, an atmospheric reservoir, a stroke simulator, the stroke simulator comprising a simulator piston operatively coupled with a brake operating member and an elastic member for imparting a stroke corresponding to the brake operating force to the simulator piston and a simulator chamber formed in front of the simulator piston, an input piston having the simulator piston therein for receiving the brake operating force from the simulator piston through the elastic member, and a pressure adjusting valve which activates according to the displacement of the input piston or the simulator piston to adjust the hydraulic pressure supplied from the hydraulic pressure source to a value corresponding to the brake operating force, a master cylinder having a master piston and activated by the fluid pressure from the pressure adjusting valve, and an auxiliary piston provided between the input piston and the master piston with its front protruding into a fluid chamber for applying the output fluid pressure from the pressure adjusting valve to the master piston of the master cylinder, the auxiliary piston being pushed by the input piston upon failure of a hydraulic line connecting to the fluid chamber and transmitting the brake operating force to the master piston.
According to the present invention, the vehicle brake hydraulic pressure generating device is provided with a shutoff valve which shuts off the communication between the simulator chamber and the atmospheric reservoir when the stroke of the input piston relative to a housing for the input piston exceeds a predetermined value and a check valve which permits the flow of brake fluid from the atmospheric reservoir to the simulator chamber are provided.
As an alternative solution, the vehicle brake hydraulic pressure generating device is provided with a shutoff valve which shuts off the communication between the simulator chamber and the atmospheric reservoir when the stroke of the input piston relative to the auxiliary piston exceeds a predetermined value or a shutoff valve which shuts off the communication between the simulator chamber and the atmospheric reservoir when the stroke of the pressure adjusting valve exceeds a predetermined value.
If the hydraulic pressure source fails, the input piston makes a stroke by a predetermined value or over relative to the housing during brake operation. Thus, the shutoff valve shuts off communication between the simulator chamber and the atmospheric chamber. This seals brake fluid in the simulator chamber. Since the sealing is done in a situation in which reaction force to the brake operating force is scarcely produced, the simulator piston scarcely makes a stroke in this stage. Thereafter, the hydraulic pressure produced in the simulator chamber restricts the stroke of the simulator piston, so that an unavailable stroke is suppressed to a small level.
When the brake is relaxed, brake fluid flows from the atmospheric reservoir into the simulator chamber through the check valve without restriction, so that the simulator piston returns quickly to the original position. Thus, even if the hydraulic pressure source fails during brake operation and quick return and subsequent quick brake operation are carried out, an unavailable stroke is suppressed.
In an arrangement in which communication between the simulator chamber and the atmospheric chamber is shut off by a shutoff vale which closes if the stroke of the input piston relative to the auxiliary piston exceeds a predetermined value, or if the stroke of the pressure adjusting valve exceeds a predetermined value, too, brake fluid is sealed in the simulator chamber by the same function as above if the hydraulic pressure source fails. Thus the stroke of the simulator piston is restricted by the sealed hydraulic pressure. This suppresses an unavailable stroke to a small level. If the hydraulic pressure source fails during brake operation and quick return of the brakes are carried out thereafter, the stroke of the input piston returns to a predetermined value or less relative to the auxiliary piston (or the stroke of the pressure adjusting valve returns to a predetermined value or less). Thus the shutoff valve opens and the simulator piston returns quickly. Thus, the above-described check valve is not necessary.